Snowden has been caught in legal limbo in the transit zone of Moscow's Sheremetyevo airport since his arrival from Hong Kong on June 23. The U.S. has annulled his passport, and Ecuador, where he has hoped to get asylum, has been coy about offering him shelter.

Russia's President Vladimir Putin says Snowden will have to stop leaking U.S. secrets if he wants to get asylum in Russia, but adds that Snowden has no plan to quit doing so.